Prior art teaches a number of strategies for directly harnessing solar energy. Solar water heaters are especially efficient and inexpensive. Solar electricity generators include solar cells, solar Stirling engines, and arrays of heliostats or parabolic troughs that concentrate solar energy to capture heat that eventually powers a steam-driven electric generator.
A significant disadvantage of all power generation processes is the substantial inefficiency of three typical steps. The first of the three steps is converting energy from a naturally occurring form to a transportable form. The most versatile transportable energy form is electricity. Current typical solar cells for terrestrial use rarely convert even 20% of incident light energy to electricity. More than 90% of the light energy striking a dark solar cell may be lost as waste heat. Combustion of fossil fuels to generate electricity is typically less than 50% efficient. The second of the three steps is moving energy to a location where it performs work. This movement typically occurs by vehicle, pipe, or wire. Vehicles and pipes require energy inputs. High voltage transmission of electricity involves substantial losses of energy. The third of the three steps is the use of the energy to perform work. Typical air conditioners usefully employ a fraction of drawn electrical current to pump heat from a cooled interior space to an exterior space, said exterior space typically comprising the air around an exterior air conditioning unit. The air conditioning unit inevitably generates significant amounts of waste heat. Heat moved from the interior and heat generated by pump raise temperatures in the immediate vicinity of the air conditioning unit, making further cooling harder, because it increases the temperature gradient that the air conditioner must pump against. In heating applications, the third step is typically efficient, but the first and second steps remain wasteful.
A significant disadvantage of solar energy collection devices is the accumulation of waste heat in the vicinity of the energy collection, often occurring in the vicinity of spaces where cooling is desired. The rate of heat transfer between a warmer and a cooler body is proportional to the difference in temperature of said warmer and cooler bodies, regardless of insulation. Insulation reduces the rate of heat transfer for any given temperature difference, but doubling the difference in temperature will double the rate of heat transfer through any fixed insulator. Consequently, trapping or moving heat to an area adjacent to a cooled area increases the rate of return of said heat to the cooled area. Furthermore, fixed insulating layers may retard nighttime cooling
Experiments conducted by the inventor demonstrate that in full summer sun, with an ambient temperature below 35 degrees centigrade, the underside of a commercial flexible solar panel driving a water pump reaches a temperature of at least 50 degrees centigrade. In this experiment, a portion of the solar energy reaching the solar panel is diverted to run the pump, and the pump generates waste heat at a distant location. In spite of this energy transfer, the solar panel converts a large amount of solar energy to local heat. The same result is obtained by harnessing all of the power output of a solar panel to drive hydrolysis in a salt solution, presumably diverting as much energy as possible from the solar panel. All existing solar panels integrated in roofing material or awnings must have similar local heating effects. In addition, current solar panels are extremely expensive in terms of monetary cost and energy recovery. Most current solar panels take years to generate as much electricity as was required to make the solar panels.
Prior art teaches various methods for passive cooling. A plurality of patents teach evaporation of a coolant, such as water, in an open or closed system, from a surface to cool the underlying area. Jerome (U.S. Pat. No. 6,250,091) teaches evaporation of precisely applied water, the coolant, from a roof surface. Marek (U.S. Pat. No. 6,820,439) teaches evaporation of water from a film material. De Geus (U.S. Pat. No. 4,213,305) teaches a coolant other than water in a closed system. Any open evaporative cooling system using water increases local humidity, thereby decreasing evaporative cooling of human bodies, thereby increasing the perceived heat of the environment.
Prior art teaches various methods for controlling the heating effects of sunlight. A common use of metallized Mylar® places a sheet of the highly reflective material on the roof of a structure such as a recreational vehicle or mobile home. An experiment reported by the United States Geological Service demonstrates that metallized Mylar® significantly reduces heat gain. A square reflective sheet, 25 meters on each side, was placed over desert sand in the early morning. Temperatures beneath the reflective sheet remained 27 degrees centigrade (about 81 degrees Fahrenheit) while ambient temperatures reached 43 degrees centigrade (about 109 degrees Fahrenheit). The reflective sheet was removed to test a satellite based thermal sensor. Ground personnel documented that the temperature of the exposed sand surface rose to from 27 to 40 degrees centigrade within 20 minutes. This experiment demonstrates a significant cooling effect when a highly reflective surface prevents absorption of solar energy. Under this summer desert condition, a passive 13 degree centigrade cooling effect could transform an area from being oppressively hot to tolerable. Furthermore, this cooling did not occur by moving heat to a second ground level location, but by reflecting solar energy back to the sky. A portion of the reflected solar energy would leave the atmosphere and enter space.
The inventor conducted a similar experiment in 2005 using Mylar affixed to tarps to cover a sunroom, finding that peak summer temperatures could be lowered 10 to 15 degrees Centigrade. Disadvantageously, the apparatus is hard to deploy, the metallized Mylar® deteriorates quickly in wet weather, and reflections from the metallized Mylar® are blinding, so that such sheets must be carefully deployed to avoid reflecting light into the eyes of neighbors or drivers. Other significant disadvantages of metallized Mylar® and similar films are noise generated by distortion in the wind, high flammability, and high electric conductivity. Metallized Mylar® sheets could attract lightening and burst into flames following a strike.
Prior art teaches a set of passive solar principals for home construction. First, a roof may overhang a window facing the equator to such an extent that the roof shades the window from summer sunlight arriving at a high angle, but in the winter permits lower angle incident solar radiation to penetrate the window. In areas with snow cover, some additional solar radiation penetrates the window after reflection from the snow surface. Second, the energy of sunlight entering a window may be captured by absorption in a high thermal mass object, such as black stone or a water mass. Third, window shutters, shades, blinds, or coatings may be used to selectively permit or block radiant energy transfers through a window. A window shade may be open during the day and closed at night to improve heating, for instance. Fourth, metallized polymer sheets, such as Mylar®, are commonly incorporated as insulating materials in fixed positions within well protected layers of construction materials. These reflective sheets reflect radiant heat back to its source. Similar sheets are not used for fixed exterior applications because rain, hail, and blown fine particulate matter rapidly damage the reflective coating or the plastic backing. Furthermore, fine particulate matter that settles on a reflective surface slowly degrades the reflective performance of the surface.
Prior art teaches a number of additional passive solar techniques. Uecker (U.S. Pat. No. 4,838,038) teaches that a cooling appliance may be shaded to reduce the temperature gradient against which it pumps heat. Hicks (U.S. Pat. No. 4,184,295) teaches that a window may be shaded by an awning to reduce the sunlight entering a room through said window. Pardo (U.S. Pat. No. 4,461,277) teaches that a window may have a heat absorbing surface that can be rotated to the outside to prevent interior heating, or to the inside to increase interior heating. Gillery (U.S. Pat. No. 4,235,048) teaches that a film applied to an interior glass surface may absorb or reflect sunlight to prevent warming of the room having said window. Falicoff (U.S. Pat. No. 4,877,675) teaches that a transparent color changing sheet passively controls the temperature of a greenhouse.
Prior art teaches a number of methods related to ceilings and roofing. A white roof coating creates a fixed partially reflective roof. This roof design will reflect large amounts of incident light, thereby cooling the roof and reducing conductive heating of the area covered by the roof. This design is in use in energy efficient demonstration homes in Florida. A first drawback of a fixed partially reflective roof is that the roof radiates a reduced amount of heat at night, compared to a dark roof, following the general principle that good reflectors are poor emitters. A second drawback is that a fixed partially reflective roof reflects large amounts of warming sunlight on cold days. A third drawback of a fixed partially reflective roof, as embodied by a white coated roof, is that on hot days a portion of the sunlight striking the roof is scattered and strikes and warms other objects in the vicinity of the roof, and that a significant portion of the sunlight striking the roof is absorbed and not reflected. Falicoff (U.S. Pat. No. 4,877,675) teaches temperature sensitive changes in the color and opacity of a reflective sheet, overcoming the first two drawbacks but not the third.
Prior art describes a number of mechanisms for temperature sensitive displacement of an object. The most ubiquitous are bimetallic strips, commonly used in thermostats as a component of a physical switch that controls a heating or cooling appliance. Generally, bimetallic strips provide high power, low speed movement. Another set of temperature sensitive mechanisms for motion control include devices that use vapor pressure to shift liquids and gases, and therefore mass balances. Yet another set of temperature sensitive mechanisms for motion control include electromechanical devices.
Prior art teaches that clear, durable coatings of fluoropolymers, such as Teflon® and Tefzil® protect solar panels from weather. A solar panel so enclosed receives light, is as flexible as the silicon substrate, endures impact by hail, is non-flammable, and does not conduct electricity.